On Tue, Dec 30, 2025 at 6:51 AM Jiri Olsa <[email protected]> wrote:
>
> Following changes need to lookup trampoline based on its ip address,
> adding hash table for that.
>
> Signed-off-by: Jiri Olsa <[email protected]>
> ---
> include/linux/bpf.h | 7 +++++--
> kernel/bpf/trampoline.c | 30 +++++++++++++++++++-----------
> 2 files changed, 24 insertions(+), 13 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 4e7d72dfbcd4..c85677aae865 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1325,14 +1325,17 @@ struct bpf_tramp_image {
> };
>
> struct bpf_trampoline {
> - /* hlist for trampoline_table */
> - struct hlist_node hlist;
> + /* hlist for trampoline_key_table */
> + struct hlist_node hlist_key;
> + /* hlist for trampoline_ip_table */
> + struct hlist_node hlist_ip;
> struct ftrace_ops *fops;
> /* serializes access to fields of this trampoline */
> struct mutex mutex;
> refcount_t refcnt;
> u32 flags;
> u64 key;
> + unsigned long ip;
> struct {
> struct btf_func_model model;
> void *addr;
> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> index 789ff4e1f40b..bdac9d673776 100644
> --- a/kernel/bpf/trampoline.c
> +++ b/kernel/bpf/trampoline.c
> @@ -24,9 +24,10 @@ const struct bpf_prog_ops bpf_extension_prog_ops = {
> #define TRAMPOLINE_HASH_BITS 10
> #define TRAMPOLINE_TABLE_SIZE (1 << TRAMPOLINE_HASH_BITS)
>
> -static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE];
> +static struct hlist_head trampoline_key_table[TRAMPOLINE_TABLE_SIZE];
> +static struct hlist_head trampoline_ip_table[TRAMPOLINE_TABLE_SIZE];
>
> -/* serializes access to trampoline_table */
> +/* serializes access to trampoline tables */
> static DEFINE_MUTEX(trampoline_mutex);
>
> #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
> @@ -135,15 +136,15 @@ void bpf_image_ksym_del(struct bpf_ksym *ksym)
> PAGE_SIZE, true, ksym->name);
> }
>
> -static struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
> +static struct bpf_trampoline *bpf_trampoline_lookup(u64 key, unsigned long
> ip)
> {
> struct bpf_trampoline *tr;
> struct hlist_head *head;
> int i;
>
> mutex_lock(&trampoline_mutex);
> - head = &trampoline_table[hash_64(key, TRAMPOLINE_HASH_BITS)];
> - hlist_for_each_entry(tr, head, hlist) {
> + head = &trampoline_key_table[hash_64(key, TRAMPOLINE_HASH_BITS)];
> + hlist_for_each_entry(tr, head, hlist_key) {
> if (tr->key == key) {
> refcount_inc(&tr->refcnt);
> goto out;
> @@ -164,8 +165,12 @@ static struct bpf_trampoline *bpf_trampoline_lookup(u64
> key)
> #endif
>
> tr->key = key;
> - INIT_HLIST_NODE(&tr->hlist);
> - hlist_add_head(&tr->hlist, head);
> + tr->ip = ftrace_location(ip);
> + INIT_HLIST_NODE(&tr->hlist_key);
> + INIT_HLIST_NODE(&tr->hlist_ip);
> + hlist_add_head(&tr->hlist_key, head);
> + head = &trampoline_ip_table[hash_64(tr->ip, TRAMPOLINE_HASH_BITS)];
For key lookups we check that there is no existing trampoline for the
given key. Can it happen that we have two trampolines at the same IP
but using two different keys?
> + hlist_add_head(&tr->hlist_ip, head);
> refcount_set(&tr->refcnt, 1);
> mutex_init(&tr->mutex);
> for (i = 0; i < BPF_TRAMP_MAX; i++)
> @@ -846,7 +851,7 @@ void bpf_trampoline_unlink_cgroup_shim(struct bpf_prog
> *prog)
> prog->aux->attach_btf_id);
>
> bpf_lsm_find_cgroup_shim(prog, &bpf_func);
> - tr = bpf_trampoline_lookup(key);
> + tr = bpf_trampoline_lookup(key, 0);
> if (WARN_ON_ONCE(!tr))
> return;
>
> @@ -866,7 +871,7 @@ struct bpf_trampoline *bpf_trampoline_get(u64 key,
> {
> struct bpf_trampoline *tr;
>
> - tr = bpf_trampoline_lookup(key);
> + tr = bpf_trampoline_lookup(key, tgt_info->tgt_addr);
> if (!tr)
> return NULL;
>
> @@ -902,7 +907,8 @@ void bpf_trampoline_put(struct bpf_trampoline *tr)
> * fexit progs. The fentry-only trampoline will be freed via
> * multiple rcu callbacks.
> */
> - hlist_del(&tr->hlist);
> + hlist_del(&tr->hlist_key);
> + hlist_del(&tr->hlist_ip);
> if (tr->fops) {
> ftrace_free_filter(tr->fops);
> kfree(tr->fops);
> @@ -1175,7 +1181,9 @@ static int __init init_trampolines(void)
> int i;
>
> for (i = 0; i < TRAMPOLINE_TABLE_SIZE; i++)
> - INIT_HLIST_HEAD(&trampoline_table[i]);
> + INIT_HLIST_HEAD(&trampoline_key_table[i]);
> + for (i = 0; i < TRAMPOLINE_TABLE_SIZE; i++)
> + INIT_HLIST_HEAD(&trampoline_ip_table[i]);
> return 0;
> }
> late_initcall(init_trampolines);
> --
> 2.52.0
>
